Veiling glare are mirror-like images of an object projected onto a window. The mirror-like image is caused when light is transmitted through a window onto the object. The light reflects off the object onto the inner surface of the window.
Veiling glare is a phenomenon which is commonly observed inside an automotive vehicle. In particular, light penetrates the windshield and strikes the dashboard, the dashboard (“D”) reflects the light onto the interior surface of the windshield (“W’) as depicted in FIG. 1. Thus, what is superimposed onto the windshield is a mirror image of the dashboard. The mirror image of the dashboard imposed on the windshield can lower the contrast of road scene.
With reference now to FIG. 2, a perspective view showing the relationship between incident angles and reflectance from the panel seen on the windshield “W” of an automotive vehicle is provided. The windshield “W” is angled with respect to the dashboard “D”. The dashboard “D” is shown disposed on a generally horizontal plane. The windshield “W” may be angled 20 to 40 degrees with respect to the dashboard “D”. The driver's eye is indicated by “DE” and the reflections from the dashboard “D” are indicated by the uniform and dashed lines.
FIG. 2 illustrates that lights enters the driver's eye from both above and below the driver's field of view. In such a windshield “W” and dashboard “D” configuration, angles ϕ1 and ϕ2 ϕ2 are the angles between the dashboard “D” and the windshield “W”, and indicate the directions of light coming from above and below the panel. Both ϕ1 and ϕ2 have a range of 0 to 25 degrees, and thus, the incident angle of lights that contribute to veiling glare has a range of 40 to 80 degrees.
When the incident angle of lights contributing to veiling glare has a range of 40 to 80 degrees, the reflectivity of P-polarized lights is much lower than that of S-polarized lights at the air-glass boundary by calculating the Fresnel reflection coefficients. A relationship between the power of reflectivity and the incident angles is provided in the chart shown in FIG. 3. The chart is formulated with the assumption that the refractive indexes of the glass/windshield is 1.5 and the refractive index of air is 1.0. Accordingly, reducing veiling glare may be accomplished by controlling the reflectivity of P-polarized lights. With reference again to FIG. 3, it is seen that the reflectivity for P-polarized light vanishes at Brewster's angle.
As is demonstrated in FIGS. 2 and 3, veiling glare is influenced by the reflectance of the dashboard. Thus, veiling glare may be reduced by having a panel which is colored darkly. It is known that darkly colored panels have low-reflectivity, but also absorbed a larger spectrum of light and thus generates heat. Further, such an approach limits the colors which may be offered as bright colored dashboard panels may increase veiling glare. As used herein, “brightly colored” refers to a panel configured to reflect wavelengths having a wavelength between 380-750 nm.
Attempts have been made to reduce veiling glare. Such attempts include the use of an absorbing polarizing layer mounted on top of a reflecting layer. The reflecting layer includes reflective or scattering pigments to increase the brightness of the vehicle interior. However, the brightness is reduced with the absorbing polarizing layer mounted on top thereof.
Accordingly, it remains desirable to have a brightly colored panel configured to reduce veiling glare while maintaining the brightness of its color by utilization of a high reflectivity structure.